A DC to DC (direct current to direct current) converter using a sliding mode is disclosed in “On the practical design of a sliding mode voltage controlled buck converter”, S. C. Tan, et. al., IEEE Transactions on Power Electronics, Volume 20, pp. 425-437, 2005. A switch of the DC to DC converter by monitoring an output voltage “vc” and a current “ic” flowing in a smoothing capacitor without using an external clock. The DC to DC converter can quickly respond to variation of the current flowing in a load unit connected to the DC to DC converter even without the external clock.
However, the DC to DC converter monitors the output voltage “vc” and the current “ic” individually. Therefore, circuit size of the DC to DC converter becomes larger.